136 THE GENERAL ANATOMY OF THE CERCOPITHECIDAE [.SECT. A 



(a sheet of fibres not found in the true Lemurs). The fibular part 

 of the aponeurosis becomes attached deeply in the region of the 

 fifth metacarpal bone (proximal part). A deeply-placed inter- 

 mediate aponeurosis runs towards the first digit, but the original 

 "fasciculus hallucis" (seen in Lemurs) does not reappear. The 

 outstanding point is the strengthening of the middle parts of the 

 aponeurosis, and this feature is directly related to the environment 

 of the animals concerned, for it is greatest in those, such as Cynoce- 

 phalus hamadryas, of terrestrial rather than purely arboreal habits. 



(ii) The M. flexor brevis digitorum arises partly from the 

 plantar fascia. In a young male Cynocephalus mormon, I found 

 an arrangement identical with that represented by Dr Sawalischin 1 . 

 Thus the superficial head (derived from the plantar fascia) fur- 

 nished a tendon to the second digit, and an indefinite fascial 

 expansion directed towards but failing to reach the third digit. 

 The deep head arose from the tendon of the M. flexor longus digi- 

 torum (flexor tibialis) and provided perforated tendons for the 

 third, fourth and fifth digits. 



(iii) The M. flexor longus digitorum supplies the four outer 

 digits and is joined by a M. flexor accessorius which has but one 

 head of origin. 



(iv) M. flexor hallucis longus (flexor fibularis) is conjoined 

 with the tendon of the preceding muscle, and contributes tendons 

 to the hallux and three next digits, but not to the fifth toe. 



While the conditions in general resemble those already noted 

 in the Lemur, a few points of distinction may yet be found. Thus 

 the differences are least in the upper limb, and here no functional 

 divergence of note has occurred. In the lower limb, the monkey 

 shews signs of a tendency to emancipate this organ from a solely 

 arboreal function. The strengthening and increased rigidity of 

 the plantar fascia, the development of a M. flexor accessorius, 

 and the withdrawal of part of the M. flexor fibularis (from the 

 fifth toe) together with the relative shortening of the digits, all 

 point to an increased adaptation of the foot to a truly planti- 

 grade (as contrasted with a prehensile) function. 



A muscle in the orbital cavity named M. choanoides (or M. 



1 Morphologisches Jahrbuch, Band xlii. Heft 4, S. 598, Fig. 20b. 



